I think this is a case of she did it as long as she could muster and now she just can't manage to do it any more. Think about it, if it's really that bad for her, she'll end up yakking...definitely a mood killer. I have tried for my husband and I just can't do it. Once you get to the point where you have become nauseated by it, it's impossible to keep doing it.
I can tell you a friend of mine owns an adult novelty store and told me that she has found that more men are comfortable w/ the taste of ejaculate (theirs or someone elses...tim..I know) that are most women.
It has been proven that womens tastebuds are a bit different than mens. I can't remember the basics of it, but that would explain why it's so different to her. I can also tell you that IMO ejaculate has a very strong smell...and thinking about it as I post this is enough to make me feel queesy...sorry.
I don't know whether to pat you on the back for being such a trooper, but anything less than fresh on my end, I won't let my husband touch me with someone elses 10' pole!!
Good luck and try not to take it personally...it likely has more to do with she tried as long as she could rather than she just doesn't care to indulge in it any more.